1. Field of the Invention
The present invention relates to an ink jet head, which is characterized in its capability of judging an ink filling state in an ink passage, for instance, in an ink jet head mounted on an ink jet recording apparatus which is applied to a printer or a fax machine, and to an ink jet recording apparatus provided with the ink jet head.
2. Description of the Related Art
Conventionally, there is known an ink jet recording apparatus that records characters and images on a medium to be recorded using a recording head which ejects ink from a plurality of nozzles. In such an ink jet recording apparatus, the recording head which opposes the medium to be recorded is provided in a head holder, and this head holder is mounted on a carriage to be scanned in a direction orthogonal to a conveying direction of the medium to be recorded.
A schematic exploded view of an example of such a recording head is shown in FIG. 8 and a sectional view of main parts of the same is shown in FIG. 9. As shown in FIGS. 8 and 9, a plurality of grooves 102 are provided in parallel with each other in a piezoelectric ceramic plate 101, and each groove 102 is separated by side walls 103. An end portion in a longitudinal direction of each groove 102 is extended to an end surface of the piezoelectric ceramic plate 101 and the other end portion is not extended to the other end surface, making the groove 102 to be gradually shallow. In addition, electrodes 105 for applying a driving electric field are formed on surfaces on opening-side surface of both the side walls 103 in each groove 102 throughout its longitudinal direction.
A cover plate 107 is bonded on the opening side of the grooves 102 of the piezoelectric ceramic plate 101 using adhesive 109. The cover plate 107 includes an ink chamber 111 to be a recessed portion communicating with the other end portion where each groove 102 is shallow and an ink supply port 112 that is bored from the bottom portion of this ink chamber 111 in a direction opposite to the grooves 102.
In addition, a nozzle plate 115 is bonded to an end surface of a bonded body of the piezoelectric ceramic plate 101 and the cover plate 107 in which the grooves 102 are opened, and nozzle openings 117 are formed in positions opposing the respective grooves 102 of the nozzle plate 115.
Note that, a wiring substrate 120 is fixed to the surface of the piezoelectric ceramic plate 101 on the other side of the nozzle plate 115 and on the other side of the cover plate 107. Wiring 122 connected by each electrode 105, bonding wires 121 and the like is formed on the wiring substrate 120, and a driving voltage can be applied to the electrodes 105 via this wiring 122.
In a recording head configured in this way, when each groove 102 is filled with ink from the ink supply port 112 and a predetermined driving electric field is caused to act on the side walls 103 on both sides of the predetermined groove 102 via the electrode 105, the side walls 103 are deformed to change the volume of the predetermined groove 102, whereby the ink in the groove 102 is ejected from the nozzle opening 117.
In such a recording head, oscillation energy generated on a side wall is transmitted to ink in a passage, to thereby realize ink ejection. For realizing the above, it is necessary that ink be sufficiently filled in the passage without producing any gap. However, for instance, in the case where the first ink filling is conducted to the recording head or ink is exchanged, a part of the passage is not occasionally filled with ink or the passage occasionally involves generation of air bubbles. When the passage contains such filling defect, the oscillation energy generated on the side wall is not sufficiently transmitted to ink, thereby causing printing defect in which ink is not ejected and the like.
Conventionally, in order to prevent such printing defect from causing, actual printing is carried out on a recording medium such as a piece of paper or the like in advance, and there is made a judgment through visual observation whether all nozzles properly eject ink, and then such a treatment as to refill ink has been performed in the case of containing defect. However, there are problems that a large amount of time and effort as well as consumption of ink and recording mediums used for the verification are required.
In addition, as a method of automatically detecting such printing defect in advance, there is devised an apparatus in which, for instance, an ejected ink drop is detected using an optical method, to thereby judge whether ink filling has been properly conducted or not. However, the method still leaves the consumption of ink and needs another means for detecting the ink drop. Therefore, there is a problem in that the apparatus is complicatedly constructed.
The present invention has been made in view of the above, and an object of the present invention is to provide an ink jet head and an ink jet recording apparatus, provided with means for easily judging an ink filling state of a printing head, with which ink and recording mediums for verification are not consumed.
To solve the above-described problems, according to a first aspect of the present invention, there is provided an ink jet head in which a driving voltage is applied to an electrode, provided on a side wall of an ink passage formed on a piezoelectric ceramic plate, to change a volume of the ink passage, thereby ejecting ink, filled with the interior thereof through a nozzle opening; the ink jet head characterized by comprising: a signal processing means for processing a piezoelectric signal generated on an electrode provided on each of the side walls of the ink passage; a selection means composed of a group of switches that are equipped for connecting the electrode, provided on each of the side walls of the ink passage, with any one of the driving voltage, a reference voltage and the signal processing means; and a control means for controlling the selection means, and the control means is provided with a judging means for judging a filling state of ink in the ink passage through processes in which the selection means is controlled, one of the side walls that are adjacently disposed in the ink passage is driven and a piezoelectric signal that is generated on the other one of the side walls is detected.
According to a second aspect of the present invention, in an ink jet head of the first aspect, there is provided an ink jet head characterized by comprising a diagnosis signal generating means for generating a diagnosis signal for driving the side walls of the ink passage; and a signal switching means for selecting any one of the driving voltage and the diagnosis signal to connect with the selection means, and the diagnosis signal is connected with the selection means by the signal switching means in detection of a filling state of ink and the diagnosis signal is applied to one of the side walls adjacently disposed, selected by the selection means.
According to a third aspect of the present invention, in an ink jet head of the second aspect, there is provided an ink jet head in which the driving means is composed of a pulse generating circuit.
According to a fourth aspect of the present invention, in an ink jet head of the second aspect, there is provided an ink jet head in which the driving means is composed of a sine wave generating circuit.
According to a fifth aspect of the present invention, in an ink jet head of the second aspect, there is provided an ink jet head in which the driving means is composed of a sweep signal generating circuit.
According to a sixth aspect of the present invention, there is provided an ink jet recording apparatus having an ink jet head in which a driving voltage is applied to an electrode, provided on a side wall of an ink passage formed on a piezoelectric ceramic plate, to change a volume of the ink passage, thereby ejecting ink, filled in the interior thereof through a nozzle opening, the ink jet recording apparatus characterized by comprising: a signal processing means for processing a piezoelectric signal generated on an electrode provided on each of the side walls of the ink jet head; a selection means composed of a group of switches that are equipped for connecting the electrode, provided on each of the side walls of the ink passage, with any one of the driving voltage, a reference voltage and the signal processing means; and a control means for controlling the selection means, and the control means is provided with a judging means for judging a filling state of ink in the ink passage, through processes in which the selection means is controlled, one of the sidewalls that are adjacently disposed in the ink passage is driven and a piezoelectric signal that is generated on the other one of the side walls is detected.
According to a seventh aspect of the present invention, in an ink jet recording apparatus of the sixth aspect, there is provided an ink jet recording apparatus characterized by comprising: a diagnosis signal generating means for generating a diagnosis signal for driving the side walls of the ink passage; and a signal switching means for selecting any one of the driving voltage and the diagnosis signal to connect with the selection means, and the diagnosis signal is connected with the selection means by the signal switching means in detection of a filling state of ink and the diagnosis signal is applied to one of the side walls adjacently disposed, selected by the selection means.
According to an eighth aspect of the present invention, in an ink jet recording apparatus of the seventh aspect, there is provided an ink jet recording apparatus in which the driving means is composed of a pulse generating circuit.
According to a ninth aspect of the present invention, in an ink jet recording apparatus of the seventh aspect, there is provided an ink jet recording apparatus in which the driving means is composed of a sine wave generating circuit, which is described in claim 6.
According to a tenth aspect of the present invention, in an ink jet recording apparatus of the seventh aspect, there is provided an ink jet recording apparatus in which the driving means is composed of a sweep signal generating circuit.
The present invention is capable of easily making a judgment regarding the ink filling state of a printing head without consuming any ink and recording medium that are used for verification, resulting in leading an expectation to exhibit a considerable effect in reduction of printing cost and enhancement of printing quality.